Study On Mechanisum Of Moisture-heat-stress Coupling For Frozen Soil And Engineering Application

China is a country with wide distribution of frozen soil,of which fifty-three percent is seasonally frozen soil.In seasonally frozen regions,freezing and thawing action is the main cause responsible for the destruction of pavements,canals,slopes,pipelines and so on,which is closely linked to the temperature gradient,water transport and stress.Due to the coupling mechanism is complicated and involves many subjects such as heat transfer,hydromechanics,physical chemistry,plastoelasticity mechanics,etc,so there are excessive parameters in the coupling models which need to be concerned to describe this phenomenon.Many parameters adopted in these models are not easy to determine accurately,which may hinder wide engineering applications of these models.In order to prevent and solve the problem of freezing and thawing action effectively,we must understand the mechanism of freezing and thawing action,and then establish the valid numerical simulation model which can provide a good reference to the design of the projects in cold regions.The main research of this paper is multi field coupled modelling of saturated frozen soil and analysis of engineering examples in seasonally frozen regions.The main contents in this paper are as follow:(1)Based on the well-known Harlan's theory,a simple moisture-heat coupling model is proposed initially to quantify the coupled moisture and heat transport performance of soil in terms of the central temperature and porosity.Then regard the soil as elastomer to obtain the relationship between frost heave and porosity,which can link hydraulic field and stress field.Next,the governing equations can be solved numerically by the well-known Galerkin method and finite difference method to get the discrete equation and coefficient matrix.Finally,the mathematical modules of COMSOL Multiphysics are further employed to solve the governing equations of temperature and hydraulic field numerically.To validate our coupling model,a thorough experimental data is also carried out to compare with our simulation results.(2)The clay soil was taken from the field of the Beiyin Canal built in Daqing region which was used to conduct a model test with the ratio of 1:10.Some data can be obtained from the model test such as temperature,maximum frost heave,maximum frost depth which is used to validate numerical simulation results.Then take the Beiyin Canal for example,some numerical simulation results like temperature field,hydraulic field,stress field,the maximum frost heave,the maximum frost heave can be calculated by finite element software which can provide some scientific basis to the internal rules of the canal in seasonally frozen regions.(3)Based on the strength reduction method,taking the Harbin-Dalian High-speed Railway slope for instance,the safety factor of slope with different water content is calculated under different freezing and thawing cycles considering the coupling field of temperature,hydraulic and stress.Comprehensive analysis the effect of water content,freezing and thawing cycles,elastic module,cohesion and internal friction angle to the slope safety index.